The SLO3 channel is a member of the high conductance SLO potassium (K+) channel family and is activated by both voltage and intracellular pH (pHi). The SLO3 channel is found only in mammals and is located exclusively in testis. We found that slo3 is a rapidly evolving gene like many genes that govern male reproduction. Our preliminary results show that SLO3 is present in mature sperm and is modulated by protein kinase A (PKA). We will use a combination of immunohistochemistry, genetics, molecular biology and electrophysiology to study the role of this particular ion channel in the physiology of the sperm. To further elucidate its role in fertility we will generate and analyze a gene knock-out (K/O) of SLO3 channels in mouse. A knock-out of the Slo3 gene will allow us to verify the identity of the K+ current that we observe in mature sperm and spermatocytes by comparing the K+ currents present in wild-type and mutant animals. A SLO3 knock-out will also allow us to determine the functional role of the channel in sperm physiology and behavior. Thus, we will examine the phenotype resulting from the loss of SLO3 channels with respect to the fertility of the K/O mouse, the production of sperm cells, sperm motility, sperm capacitation, the acrosome reaction and volume regulation of sperm. The significance of these studies are: 1. This study will contribute to our understanding of the role that K+ channels play in critically important events in sperm physiology such as motility, capacitation, the acrosome reaction and crucial osmotic control. 2. Studies of SLO3 channels may contribute to in vitro fertilization (IVF) techniques. Knowledge of the electrical properties of sperm and the essential aspects of the external ionic environment may have important implications for improving the efficiency of clinical IVF procedures. 3. SLO3 channels may be a pharmacological target useful in male contraception. 4. Genetic variation in the Slo3 gene may affect male fertility. PUBLIC HEALTH RELEVANCE: The rapidly evolving slo3 gene encodes a high conductance K+ channel found only in mammals and located exclusively in male germ cells. Our preliminary results show activation by both pHi and voltage, and its probable modulation by PKA, properties which suggest a key role in mammalian sperm physiology. Using a variety of molecular, physiological, and gene knock-out techniques we will reveal the function of these ion channels and their involvement in fertilization, information that may impact the field of in vitro fertilization and contraception.